The present invention relates generally to an improved safety system for a hydraulic punch and/or press. More specifically, the present invention pertains to an electrical circuit design which provides improved reliability and increased worker safety. This improvement to reliability and safety is obtained through the elimination of the frequent relay terminal failures that occur with the present safety systems.
U.S. Pat. No. 4,391,358, issued in 1983 to Virgil Haeger, (the xe2x80x9cHaeger patentxe2x80x9d), and presented a design for a hardware punch and/or press which included a safety mechanism that prevented an operator""s hand or finger from being crushed by the machine when in use. Although the Haeger patent design attempted to remedy a common workplace hazard, the design ultimately failed to realize the level of safety desired. Specifically, due to the relay configuration of the Haeger design, high current loads were passed through a series of low voltage relays resulting in frequent relay failure. A consequence of such relay failures was an unreliable safety system that could potentially lead to the serious injury of a worker. Therefore, there is a need to provide a safety system with excellent reliability due to an improved design of a hydraulic punch and/or press safety system.
The present invention relates to a safety system for a hydraulic punch and/or press. Specifically, the invention includes an interface between a low voltage safety circuit, contained within the press, to the high voltage control circuit of the machine. Electrical continuity in the low voltage safety circuit is required before the high voltage control circuit provides the necessary current to a hydraulic solenoid valve that allows the press to be lowered. If the electrical continuity in the low voltage safety circuit is broken, the downward movement of the punch and/or press will immediately cease. The electrical resistance of an operator""s hand or finger is sufficient to break the electrical continuity of the safety circuit, eliminating the risk of injury to the operator.
Interfacing the low voltage safety circuit with the high voltage control circuit presents the difficulty that existing press designs were unable to overcome. The existing presses interface the low voltage safety circuit to the high voltage control circuit through a relay. However, relay failure was frequent as a result of the low voltage relay terminals passing the high current demanded by the hydraulic valve solenoid. Additionally, the safety circuit must operate at low voltage in order to ensure the electrical resistance of an operator""s hand or finger will be sufficient to break the safety circuit continuity.
The present invention overcomes the frequent relay failure of existing presses through the incorporation of two (2) high voltage relays into the high voltage control circuit, thereby splitting the high voltage circuit into a low current region and a high current region. This is accomplished by having a low voltage relay that is controlled by the low voltage safety circuit that when actuated, passes a high voltage, low current to actuate an intermediate high voltage, low current, relay. The high voltage low current relay, when actuated, passes a high voltage, high current to the hydraulic valve solenoid to pressurize and activate the press. The high voltage, low current relays are much more capable of reliably passing the current necessary to actuate the high voltage, high current.